addloins creates a new instance, and adds it to the
list of instances pointed to by ptfig->LOINS. The new instance is
added in front of the list, and becomes itself the list head.
The parameter insname fills the INSNAME field of the loins
structure.
The ptmodel is used for two purposes. First, the ptmodel->NAME
fills the FIGNAME field. Second, the connectors of the figure pointed
to by ptmodel are duplicated in the LOCON field, but the signals
linked to each connector are the one given in the sigchain argument. See
chain(3) for details on chain_lists.
The matching is done in order, it means that the first connector is linked
to the first signal of the sigchain, and so on. Care must be taken when
instanciating in order to warranty the validity of the netlist.
For details on the structure, see loins(3).